Laws and rulings on school uniforms

In the United States, a few states have regulations declaring that public schools must allow students to opt out of uniform policies. The state of Massachusetts prohibits dress codes in public schools by declaring that schools may not "abridge the rights of students as to personal dress and appearance."

In 1969, the United States Supreme Court ruling in Tinker v. Des Moines Independent Community School District affirmed students' rights to free expression in public schools.

In North America, i.e. the United States and Canada, school uniforms are generally not used in public (e.g. state-sponsored) schools. However, independent schools often have school uniforms. In the 1990s, there was a trend toward (re-)introducing uniforms in American public schools, and especially so in low-income areas. This was at first motivated by a need to counter "gang clothing", but has later also been seen as a way of improving morale and discipline. Those arguments are controversial among many parents, and that fad seems to have peaked. The American kids who are most likely to wear a school uniform today are either very poor or very rich.

Proponents of uniforms argue:

they reduce cliques (or gangs) and peer-envy based on clothes
they allow the student to focus on schoolwork rather than on socialising
they add a professional air to the school environment, resulting in better morale
parents don't have to spend on vogueish brand attire. They can buy several pieces of the same clothing and rotate them. They can even be later transferred to younger siblings.
Common arguments against school uniforms are:

they violate the students' right to self-expression
they are costly (this may or may not be true)
"one-size-fits-all" style does not suit all students' body shapes
they do not actually result in any scholastic improvement
many uniforms are not gender neutral, which may lead to exploitation or discrimination
(specific to present-day United States) use of public-school uniforms implies a failing school system and could even reduce property values.